1. Field of the Invention
The present invention relates generally to the field of Communication Protocol in Long Term Evolution (hereinafter LTE) systems—Layer1 (Physical Layer), and more particularly, to a system and method for sub-frame IDentification (hereinafter ID) and Frame boundary detection in LTE.
2. Description of the Related Art
In the current specification document for Third Generation Partnership Project (3GPP) TR 25.814 v 7.0.0 (2006-06), three different options for radio frame timing detection are given as Synchronization CHannel (hereinafter SCH)-based detection, Broadcast Channel (hereinafter BCH)-based detection and reference signal-based detection.
The SCH-based detection is applicable to both hierarchical and non-hierarchical SCH. With SCH based detection, the radio frame timing can be estimated by detecting the cell-specific SCH sequence in the frequency domain employing the SCH symbol timing detected in a previous step. When primary and secondary SCH are used in the hierarchical SCH, coherent detection of the cell-specific secondary SCH can be performed using the primary SCH as a reference signal.
The BCH-based detection is also applicable to both the hierarchical and non-hierarchical SCH. For BCH-based frame-timing detection, the frame-timing is detected by decoding the BCH. This may include hypothesis testing if the BCH is transmitted less frequently than the SCH. This method requires BCH reception both for the initial cell search and neighboring cell search.
The reference signal-based detection is primarily considered for the hierarchical SCH. The frame timing information is detected by the reference signal waveform (i.e., modulation pattern). In this case, the repetition interval of the reference signal waveform should be equal to the radio frame period, or 10 milliseconds.
SCH based detection requires the detection of the cell-specific SCH sequence in the frequency domain employing the SCH symbol timing detected in the previous step. As many as 512 or more cell-specific SCH sequences need to exist, and also the UE will need to detect them by using processes such as correlation, which are time consuming. Moreover, the UE needs to store these cell-specific sequences.
BCH based detection requires the BCH reception for an initial cell search, which is not desirable. However, at this time the hypothesis testing if the BCH is transmitted less frequently than the SCH has yet to be completed.
Reference signal based detection has additional dependency on the reference signal waveform (i.e., modulation pattern) detection. Only upon reading of the reference signal contents may there be reliance on the timing in this method. Also, the reference signal waveform is only scheduled to be transmitted once per 10 milliseconds. Therefore, it imposes an additional delay in the frame boundary detection. The cell search procedure should be independent of any such signal waveform detection.
Commonly assigned US Patent Publication Serial No. US20030169702A1 to Ryu et al. describes a method of cell searching in a Wideband-Code Division Multiple Access (W-CMDA) mobile communication. According to the patent publication, an “index counter” is used to continuously calculate the timing offset or offset between frame boundaries. The index counter includes a “slot counter” and a “lower counter” which are used respectively for counting the slots and the chips corresponding to a length of a number of slots. Further, the Ryu et al. publication specifies that once the position of each asynchronous cell is determined by the slot counter, it is possible to calculate the offset between them wherein, the offset is defined as the difference between asynchronous frame boundaries. Moreover, the Ryu et al. publication describes that, using a similar process the lower counter may be able to calculate the offset between the slots corresponding to each frame. It is further mentioned in the Ryu et al. publication that such an algorithm is more time efficient for cell search.
U.S. Pat. No. 6,574,267 B1 to Kanterakis et al. describes an improvement to CDMA systems employing spread-spectrum modulation between a Base Station (BS) and a Remote Station (RS). The process starts with one RS receiving broadcast common—synchronization channel data, and after determining frame timing from the frame-timing signal, the signal is transmitted from a first RS-spread-spectrum transmitter as an access—burst signal. In the Kanterakis et al. patent, the BS notifies the RS about the correct receiving of the data packets. As an example, it has been specified in the patent publication that the packet could be identified as consisting of a number of frames, and sub-frames to the frames. The frames and sub-frames are identified by specific numbers. Further, the Kanterakis et al. patent describes that the correctness of the receiving of data packets could be achieved by identifying the frames and sub-frames carrying the data packets or by identifying the frames and sub-frames that have been received as error.